//
// Created by Administrator on 2023/11/24.
//
#include "iostream"

using namespace std;

int main() {
    int n;
    cin >> n;
    int dp[n+1];
    dp[0] = 0;
    dp[1] = 1;
    dp[2] = 2;
    for (int i = 3; i <= n; ++i) {
        dp[i]=dp[i-1]+dp[i-2];
    }
    cout<<dp[n];
}
